1. Technical Field
The present invention relates to optical waveguides in general, and in particular to a method for fabricating selectively coupled optical waveguides on a substrate.
2. Description of Related Art
Although optical waveguides can be fabricated in different layers of a substrate in a stack structure, the difficulties in enabling all those optical waveguides to couple with one another can limit the usefulness of the stacked structure. In order for optical waveguides located in different layers to couple with each other, the vertical distance between them must be a fraction of the optical wavelength, and this distance is much smaller than the typical dielectric thickness required to isolate two layers.
The entire length of conventionally coupled waveguides are separated by a relatively thin dielectric layer having a uniform thickness. However, the usage of one uniform dielectric thickness across the substrate as the coupling layer does not allow for optically isolating the optical waveguides. Thus, the conventional method of utilizing a thin coupling layer limits the integration density of coupled waveguides due to the relatively large separation distances required to provide optical isolation from adjacent waveguides.
Consequently, it would be desirable to provide an improved method for fabricating coupled optical waveguides such that optical coupling can be achieved within localized areas while adequate optical isolation from other waveguide structures located in close proximity can also be attained.